• Hi Guest!
    If you appreciate British Car Forum and our 25 years of supporting British car enthusiasts with technical and anicdotal information, collected from our thousands of great members, please support us with a low-cost subscription. You can become a supporting member for less than the dues of most car clubs.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Spitfire First Autocross in my Spitfire 1500

Share this page

mikecyc72usa

mikecyc72usa

Jedi Trainee
Offline
It's been 11 years since I last stuck some numbers on one of my Triumphs and autocrossed it. So with my friends Robert and Steve we headed on down, Robert and Steve sharing Robert's 62 Spit racer, me in my 78 1500. I had a respectable showing (12th of 20 novices, and beat a 2003 Porsche 911) and was able to make my 5th run of the day my best.

The Spitfire handled great, so I think I need to get some more power. The twin SU carbs are fine, just the throttle shafts have leaks allowing air in. I also think it's time to begin researching a new exhaust. I'm running a Pacesetter header that goes to the original intermediate pipe and original muffler. Time to design something a little less restrictive but not too loud.

As for the carbs, I only have the one set, so unless I get a 2nd set, the rebushing has to wait, as my Spitfire is my only car. I do have a line on a weber downdraft, but need to wait until a friend gets back from a work trip to see if he will give me his old manifold so I can drive in the meantime.

So once the SUs are back in action, trying to figure out the next step. Do I get a hotter cam (still have stock one) or do I just work on exhaust and maybe some polishing of the intake and head? Thoughts?

Here's a link to the pics of the day.
https://www.facebook.com/album.php?aid=2089626&id=1563667116&l=1ddd0132d8
 
It all depends on what you want for power. Free flowing exhaust will help a little, a little port work will help some but this is all a give and take. Some modifications will only do so much without other modifications. Perfect example: when you bump compression you can move more air into the cylinders, means bigger cam, bigger valves, bigger carbs, better exhaust, etc, etc, etc.
I've got a head that you can directly bolt on that will bump you up to about 9.0:1 compression. with twin carbs and a stock mk3 cam, header and free flow exhaust that should give you around 75-80 hp.
 
As you know, AX'ing it is not always power ,it's getting it to the tarmac that is sometimes the winner. Make sure your suspension is set up correctly.
A lot cheaper than mods to the motor
 
I had no problems with hookup once the race tires and course warmed up. The way the course was I could run it in 2nd at redline and over a little, or snick 3rd on the back and the times were alomost identical. I needed a 2nd and a half gear. Suspension is good. Some understeer, great brakes, just a bit short on go. The Sumitomos I ran had awesome grip right to the limit, then watch out. No real warning at all, which was fun.
 
Well your running race tires you must be in a mod class, therefore, you need all the power you can get to compete in that class.
I would agree w/ you. carbs are a must do.
 
My $.02 : Don't worry about the carbs, save your nickels & dimes for a camshaft. Some more compression wouldn't hurt either. Also pick up a copy of the Comp Prep manual if you don't have one already.
 
But Randall, don't you think he needs to have the carbs up in order to spin the camshaft?
But agree that a stock camshaft (didn't see that in his original) is a hindrance to the compression and exhaust upgrades.
 
Can you reduce weight any? That's usually a cheap way to go faster, and it helps all around the course.
 
I was in FSP. The car starts sputtering above 5500 rpm, and sometimes as low as 4500. I'll get the carbs rebushed asap, then I'll know where I stand. Already have electronic ignition, electric fan, better air filters, etc. Also I don't want to go too much higher with compression as this is an everyday car that has to deal with city traffic in Austin. Like I said, it's my only car, so I need to find that balance.
 
Been 30+ years since I knocked over orange cones. Don't know what the classes are anymore
 
DNK said:
But Randall, don't you think he needs to have the carbs up in order to spin the camshaft?
Click to expand...
He's already got twin SU carbs, which are a significant upgrade over the single ZS it had originally. And while worn bushings will upset idle to some extent, they have basically no effect at full throttle.

Yes, an engine is a system, the components need to match for best performance. But with upgrades already made in breathing (intake and exhaust) and compression; IMO the camshaft would give him the most bang for the buck at this point.

Lack of carburetion is also not likely to be the reason it sputters above 4500, IMO. If it is mixture at all, it's probably lack of fuel to the carbs; but more likely (again IMO) it is ignition.

The throttle bushings on my previous TR3A were so badly worn that the throttle disc was hitting the throat instead of the idle stop. Still ran just fine, other than a tendency for the idle rpm to "hang" around 1800-2000. After rebushing, it ran just the same, except the idle would reliably come back to ~800 rpm every time.
 
Twosheds said:
Can you reduce weight any? That's usually a cheap way to go faster, and it helps all around the course.
Click to expand...
:iagree:
Not sure about the cheap part, but it sure will help you go faster, especially if you can trim the rotating weight (flywheel, etc.). My TR3 is very streetable with it's aluminum flywheel, but I don't know how much inertia a Spit 1500 needs.
https://www.s2parts.com/product.html?id=fidanza-flywheel-triumph-spitfire-1975-1980-1500

Check the Comp Prep manual before you go any higher on rpm. ISTR there is some material in there about severe oiling problems afflicting the 1500 over 6 grand.

BTW, higher compression (within reason) also helps improve fuel mileage, and reduce overheating. It's one of the very few modifications that increases power across the board by actually making the engine more efficient rather than burning more fuel. You should be able to run at least 9.5:1 on pump gas.
 
A stock Mk 3 cam is an upgrade for the 1500 engine, just have to put in cam bearings but would probably be better off going with a nice fast road cam. The sputtering could also be caused by valve float if your springs might be a little weak. A good balance job would be a good idea to keep the bottom end in once piece if your running 4-6K very much. To help handling you can swap out the rear swing spring and long axles with an earlier fixed spring and shorter axles and keep the larger front sway bar to help stiffen up the roll. Also installing the mk3 front springs will drop the front end about 1".
 
Didn't even notice the twin SU remark.So use to thinking that already.
I'll quit while I'm behind
I'll stay to the side lines know and watch and listen
 
My son got the autocross bug late last year and has spent literally thousands on his Miata and after every event he has another list of stuff to get. How much money do you want to spend for a $10.00 trophy ? (He's old enough to know better but has the $$ to do it.)

IMHO there is no way a Spitfire could be made competitive especially after adding a few modifications as more modern cars with similar mods would be much faster. Classes might favor you once in a while but most of the time you would be competing against much better/newer equipment.

Many of the suggestions on earlier replies are good but are not cheap. Secondly I would not chance my only car unless it was driven very conservatively and what fun would that be ? Bob
 
I forgot about valve springs. Time to check those. I'll check ignition, but the Pertronix is pretty reliable in my experience. I do have lowered competition springs in front, and when I redo the suspension next time (did it when I got the car and it's only been on the road 9 months) I'll throw poly bushings in. As to reducing weight, Took off the bumper overriders and the related supports, plus the big center bumper piece, which helped a lot.

I should mention the carbs are definitely worn, as I can sometimes lift off the throttle briefly at 4000 rpm on the road, then hit the throttle again and I don't have to hit it as hard to maintain speed. Dashpot oil good, etc. I typically am at 4200 rpm on the roads in TX as everything is at least 65mph speed limits. In terms of risking my only car, I have AAA and get free towing for 100 miles. As long as the car can get home, I'll be able to fix it eventually. In the meantime I'll ride my bike everywhere (still road race and time trial so it'll be good training, lol!).
 
Sounds like the carbs are pretty well toast. The HS2's have smaller throttle shafts than the other SU's so there isn't much room to play with for having them bushed. OTOH, the shafts are usually the ones to wear not the housing so it's possible just new standard shafts or even oversize shafts may fix it. Another thought too, where are you running your ignition timing at? With higher compression you need to run it more advanced and at higher RPM it needs to be advanced more. Is your vacuum advance working correctly?
 
Do you have HS2 or HS4s? The HS2 doesn't have throttle shaft bushings, but I'm pretty sure you can ream out the body and go with over size shafts. First check and see if only the throttle shafts are worn. I have gotten away with only changing the shafts. I don't think you can put bushings in the HS2. The HS4 has pushings that can be replaced, but its gonna cost $100+. There are homecooked ways of doing it for less. YMMV

I would go ahead and change out the piston springs in the carbs. There are more than one tension avaible. Call Joe Curto for advice.

The Mk III cam is pretty good cam grind, if you can find one.

This is the first time i've ever heard the solid mounted early spring is better for handling than the later swing spring. Especially since no mention was made to a camber compensator. But I'm hardly an expert.
 
Back
Top